1. Field of the Invention
The present invention relates to an active matrix substrate and a method of manufacturing the same, and more particularly to an active matrix substrate used for a flat display panel such as a liquid crystal display (LCD) panel, and a method of manufacturing the same.
2. Description of the Related Art
An active matrix substrate for a flat display panel such as a liquid crystal display (LCD) panel is provided with a plurality of switching elements such as thin film transistors together with pixel electrodes arranged to form a matrix. Such active matrix substrate using thin film transistors is referred to as TFT substrate hereinafter. In a cellular phone market, a small-sized LCD panel such as two-inch-size panel with a TFT substrate is widely used. Although a reduction in size and weight of such a super twisted nematic (STN) type LCD panel with the TFT substrate has been realized, further reduction in cost and size are needed overwhelmingly. In Japanese Patent Application Laid-open No. 2003-066474, as shown in FIG. 4, scanning lines (gate wirings) 17 and signal lines (drain wirings) are formed on a TFT substrate 11 in a manner to intersect each other at right angles (not shown). To reduce the panel size, both terminal electrodes for gate wirings and drain wirings are arranged on the same side of the TFT substrate 11.
A signal line extraction wiring 2A and a scanning line extraction wiring 2B are thus arranged to electrically connect the terminal electrodes with the signal lines and the scanning lines located on a display area of the LCD panel, respectively. A scanning driver IC 13 for driving the scanning lines and a signal driver IC 14 for driving the signal lines are mounted on the terminal electrodes through contact holes 10, respectively. On the TFT substrate 11, a color filter (hereinafter referred to as CF) substrate 9 is located so as to be opposite to the TFT substrate 11. A liquid crystal layer (not shown) is interposed between these substrates, thus constituting a liquid crystal display (LCD) panel 200.
A conventional LCD panel has a terminal structure as shown in FIG. 3, wherein a first interlayer insulating film 3 and a second interlayer insulting film 4 are formed on the extraction wiring 2. Referring to FIG. 1, which is a cross sectional view of FIG. 4 in the vicinity of an end portion of the extraction wiring 2, voids 16 tend to be generated in the first interlayer insulating film 3, though an amount of the generation is small. These voids may reach the surface of the second interlayer insulating film 4. Since a step coverage in an edge of the extraction wiring portion of the first interlayer insulating film 3 is poor, the voids tend to be generated. When the voids are generated in the first insulating film 3, the voids grow into the second interlayer insulating film 4, and reach the surface of the second interlayer insulating film 4.
In the conventional LCD panel as shown in FIG. 4, the scanning driver IC 13 and the signal driver IC 14 are separately used. For driving the LCD panel, as shown in FIG. 2, a gate voltage 18 of about 10 to 20 V is applied to a selected scanning line through the scanning driver IC 13 for about 20 μsec as a turn-on voltage or a writing voltage for the TFT, and a storage voltage or a retention voltage of about −20 to −10 V is applied for 15000 to 20000 μsec. A base voltage of the driving driver IC 13 is always maintained at the retention voltage. Furthermore, signal lines are applied with alternate voltage of about −3 to +3 V through the signal driver IC 14 as a drain voltage to prevent image persistence in the LCD.
It may be possible to integrate two diver ICs 13 and 14 into a single driver IC to reduce an area occupied for mounting the driver ICs and to achieve a cost reduction. However, in integrating the signal line driver IC and the scanning driver IC to a single driver IC, the voltages are applied to the signal line and the scanning line with one driver IC, and thus the base voltage of the driver IC is maintained at the voltage for the signal line. Furthermore, as shown in FIG. 3, for mounting the driver IC 7 on the TFT substrate, the conductive resin 6 such as an anisotropic conductive film (ACF) is used. The conductive resin 6 is not heated directly, but only the driver IC 7 is heated. The conductive resin 6 absorbs moisture thereinto because of its material nature. When the conductive resin 6 is not heated fully, the moisture remains therein. Since the driver IC 7 is superposed on and joined to the TFT substrate to be electrically connected to the terminal electrodes through the contact holes 10 with ITO film 5, the conductive resin 6 has a positional relation in which the conductive resin 6 protrudes from the driver IC 7, and an amount of remaining moisture in the conductive resin 6 becomes larger as the conductive resin 6 becomes further away out of alignment.
Because of the foregoing conditions, the gate wiring side serving as the scanning line takes a minus potential which is a base potential, as shown in FIG. 3. Since the moisture exists in the conductive resin 6, the moisture reaches the surface of the extraction wiring 2 through the voids in the first and second interlayer insulating films 3 and 4. Then, there has been a problem that the extraction wiring 2 is hydrated by hydroxide ions (OH−) generated through dissociation of the moisture, and causes a electrical disconnection.